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ENDO > Wk 5 > Flashcards

Wk 5 Flashcards

The Thyroid Gland

1
Q

What is the thyroid gland?

A

Two lobes, connected by thyroid isthmus.
- Highly vascular (highest blood flow per g of tissue)
- Ductless alveolar gland
- Largest endocrine gland

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2
Q

Where is the thyroid gland located?

A

Below the larynx and anterior, wrapping around the trachea.

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3
Q

What are the functions of the thyroid gland?

A
  1. Secretion of thyroid hormones
  2. Secretion of calcitonin
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4
Q

What is the portion of the thyroid concerned with thyroid hormone production?

A

Thyroid follicles

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5
Q

What is the structure of thyroid follicles?

A

Each follicle is surrounded by a single layer of epithelial cells and colloid (pick-staining protein rich fluid).

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6
Q

What is an inactive gland?

A
  • colloid is abundant
  • follicles are large
  • lining cells are flat
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7
Q

What is an active gland?

A
  • follicles are small
  • cells are cuboid/columnar
  • colloid is being actively reabsorbed visibly through “reabsorption lacunae”
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8
Q

What are the two major iodine containing hormones that are secreted by the thyroid gland?

A

Amine Hormones
T3 (more biologically active), T4

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9
Q

What hormone is secreted by the C cells?

A

Calcitonin

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10
Q

What is the thyroid hormone biosynthesis pathway?

A
  1. TRH release from hypothalamus
  2. Ant pit to release TSH
  3. TSH stimulates follicular cells to synthesise thyroid binding globulin (TBG)
  4. Iodide trapping
  5. Oxidation of Iodide (T.P.O)
  6. Iodination of tyrosine A.A
  7. Couple DIT’s (T4) & MIT’s (T3)
  8. Endocytosis of TBG with T3 & T4
  9. Lysosomal enzymes cleave T3, T4 out of TGB
  10. Exocytosis of T3, T4 into blood plasma
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11
Q

Which thyroid hormone has a higher affinity for receptors?

A

T3

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12
Q

Are thyroid hormones lipophilic or lipophobic?

A

Lipophilic

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13
Q

What is the process of thyroid hormones after they are synthesised?

A
  1. Enter cells and T3 binds to nuclear receptors
  2. Circulates in bound form, bound to TBG, albumin, thyroxine binding prealbumin
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14
Q

What is negative feedback loop of the thyroid hormone?

A

Hypothalamus (TRH) –> Anterior pituitary (TSH) –> Thyroid Gland (T3, T4)

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15
Q

What is the role of TSH?

A
  • increases in iodide binding
  • increased synthesis of T3, T4 and iodotyrosines
  • secretion of thyroglobulin into the colloid
  • endocytosis of colloid
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16
Q

What is the effect of the thyroid hormone on the cardiovascular system?

A
  • increased heart rate
  • increased contractility
  • increased CO and HR
  • increased blood flow
  • increased respiration
17
Q

What is the effect of the thyroid hormone on lipids?

A
  • increased lipolysis
  • decreased fat store
  • increased FFA
  • decreases the conc. of cholesterol, phospholipids, triglycerides
18
Q

What is the effect of the thyroid hormone on the muscle system?

A
  • increased protein catabolism
  • increased skeletal muscle activity
19
Q

What is the effect of the thyroid hormone on the growth system?

A
  • increased bone growth & skeletal development
  • act with GH
  • promote ossification & fusion of plates
20
Q

What is the effect of the thyroid hormone on the nervous system?

A
  • increased CNS development
  • increased reflex activity
21
Q

What is the effect of the thyroid hormone on carbohydrates?

A
  • increased glucose absorption
  • potentiate the effect of Epi & Nor epi, glucagon, GH
  • increased gluconeogenesis
  • increased glycogenolysis
  • increased blood sugar
22
Q

What are other effects of the thyroid hormone?

A
  • increased O2 consumption
  • increased basal metabolic rate (BMR)
  • increased Na, K ATPase
  • increased body temp
  • increased GI motility
23
Q

What is hyperthyroidism?

A

An overactive thyroid gland that leads to an excess of thyroid hormones.

24
Q

What are the causes of hyperthyroidism?

A
  • Thyrotoxicosis
  • Graves Disease (increased thyroid stimulating immunoglobulins; TSH receptor stimulation)
  • Increased TSH
25
Q

What are the symptoms of hyperthyroidmism?

A
  • increased BMR
  • weight loss
  • increased sweating
  • tremor
  • muscle weakness
  • exophthalmos (protruding eyes)
  • goiter (swollen neck)
26
Q

What is hypothyroidmism?

A

An underactive thyroid gland that leads to a deficiency of thyroid hormones.

27
Q

What are the causes of hypothyroidism?

A
  • thyroiditis (autoimmune; Hashimoto)
  • congenital (cretinism)
  • iodine deficiency
28
Q

What are the symptoms of hypothyroidmism?

A
  • decreased BMR
  • weight gain
  • cold sensitivity
  • myxedema (usually dryness of lower legs)
  • growth retardation
  • mental retardation
  • atherosclerosis (due to increased cholesterol)

ENDO (10 decks)

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